It has long been recognized in the pacemaker field that the connector presents a limitation on reducing the size of an implantable pacemaker device. The connector performs the important function of providing mechanical and electrical connection between the pulse generator and other circuitry of the pacemaker, and the lead or leads which carry signals in each direction between the implanted pacemaker device and the patient's heart. Improved miniaturization of pacemaker circuitry has permitted a great reduction in the size of implantable pacemaker units, including a reduction of the thickness (width) of the units.
However, for certain reasons known in the art, the size of connector portion where the proximal end of the leads are connected to the pacemaker device cannot be arbitrarily reduced without sacrificing stress concentration on the leads and/or integrity of the connection.
In a typical prior art connector for a bipolar lead, the two lead pins are received in side-by-side jacks, an arrangement that imposes a limit on reducing the connector thickness. However, thickness can be reduced by replacing the side-by-side relation with what is referred to as an "over/under" arrangement for receiving the branches, or furculae of the lead. See, for example, U.S. Pat. No. 4,180,078, to Anderson. However, for dual chamber pacemakers requiring two leads for carrying signals to and from two chambers of the heart, there is generally employed a pair of in-line connector jacks, each jack receiving a bipolar lead which has a pair of conductor areas which are connected to terminal blocks. European Patent Application 0 052 879 illustrates a bipolar in-line connector for receiving an implantable lead. Generally, in such dual chamber arrangements, each of the two conductors of a bipolar in-line lead is connected to a respective terminal block and fixed to such block by a set screw which clamps the lead pin or surface area to the terminal block. The set screws are positioned in puncture plugs which must be large enough to accommodate them, and in practice the size of the puncture plugs has heretofore placed a lower limit on the width of the connector. A typical arrangement is that the set screws are accessed through the top of the connector block, typically by first fixing the pair of connections corresponding to one of the leads, and then fixing the pair corresponding to the other lead. The two jacks are generally side-by-side and separated across the width of the connector, with the connector blocks aligned upward so as to provide the access openings at the top of the device. Thus, viewing the connector from the top, there are two pairs of in-line openings through the top of the epoxy for accessing the set screws of the terminal blocks. The jacks can be positioned one on top of the other, but then the access openings are on the sides, which is less desirable ergonomically.
It is recognized that the potential advantage of further reduction in the width of a pacemaker is contingent upon also reducing the width of the connector, which should be flush with the sides of the pacemaker can or casing. In view of the above-noted limitations on reducing the size of the connector block, there remains a great need in the art for a connector block design which enables a reduced overall pacemaker size.